I spent way too much time on this. Also posted on the OW forums.

Backstory

Sirius is an Omnic who escaped from the Australian Omnium prior to its destruction. In the wake of the fallout, Sirius became a salvager and outcast, forced to constantly move about to stay one step ahead of the Omnic-hating Junkers.

More Details

Sirius' primary role is aggressive battlefield management of both allies and enemies with a unique hodgepodge of dual-function abilities. While he's far from a good point-blank duelist, the tools at his disposal allow him to shut down highly mobile and unpredictable heroes' advances, or boost those same heroes on his own team.

• Health: 250 (50 Standard Health, 200 Armor - subject to tuning)

• Size: Approximately similar to a standing Zenyatta - basic humanoid Omnic.

Primary Weapon: Seeker Stream

• Full description: Sirius agitates the nest of Omnic parasites that serve as his weapon, releasing a multitude of lethal ground-following Seekers. They can only damage targets proximate to the ground, but have a subtle homing ability.

• Help menu description: Ground-level projectiles with subtle homing.

Fires a continuous stream of Seekers in the direction you are facing, dealing about 70 DPS. Seekers are medium speed ground-following projectiles that slightly home in towards enemies.

Seekers can only damage enemies within 1 meter of the ground (their hitbox extends that high - think a thin flare trail extending up from the projectile itself) and cannot headshot. However, they are also immune to projectile blocking abilities like Defense Matrix and Deflect.

Ability 1: Gravitic Gauntlet

• Full description: Sirius' Gravitic Gauntlet allows for manipulation of a target's momentum for a limited time. Allies are given increased speed and knockback immunity, while enemies are pulled toward the ground, slowed down and prevented from jumping while grounded.

• Help menu description: Channel to increase allies' speed or pull enemies to the ground.

A highly versatile battlefield control tool, with granularly-depleting charge akin to D.Va's Defense Matrix. It has automatic lock-on targeting, and comes with dual functionality:

• When utilized on enemies, the Gauntlet will pull them down to the ground and restrain them. Constant downward pull is applied, horizontal speed is mildly restricted, and the target becomes unable to jump if they are in contact with the ground. This synergizes strongly with Seekers, as they are only able to damage ground-proximate enemies.

• When utilized on allies, the Gauntlet will give them immunity to knockback (though not the damage from ordinarily knockback-inflicting hits), as well as giving them increased movement speed and preventing their movement speed from being reduced (e.g. from Mei's chill [but not freeze] or Symmetra's sentry turrets). The ability can be used on Sirius himself by activating it without a target.

Ability 2: Nanite Swarm

• Full description: Sirius releases a multitude of repurposed nano-scale maintenance drones towards an allied or enemy target. Allies are given a protective barrier and have their armor repaired, while enemies take damage over time.

• Help menu description: Applies a swarm that protects allies or deals damage to enemies.

Creates a rapidly-swirling cluster of nanites around a target. The swarm has 100 HP, has a slow projectile speed (requiring you to be close for consistent application), expires after 8 seconds, and can be applied to enemies or allies (yourself included). Cooldown is 7 seconds.

• When utilized on allies, it becomes an additional layer of barrier (represented by a silver color) that applies over the top of all other defense types. If the ally has armor, the nanites will use themselves to repair the armor, healing 50 Armor per second at a 2:1 nanite to armor ratio.

• When utilized on enemies, it becomes a damage over time effect, obscuring the enemy's view and dealing 25 damage per second, for a total of 200 base damage over the life of an uninterrupted Cloud. With a healer onboard or a health pack within 8 seconds' reach, the damage is negligible, but in combination with other effects it is significantly more effective, as it does not dissipate after leaving Sirius' line of sight.

Ultimate: Steel Storm

• Full description: Sirius unleashes the full power of his combined mechanisms, creating a large cloud of miniature attack drones that autonomously target and engage enemies.

• Help menu description: Creates a cloud that continually releases auto-targeting projectiles.

The Steel Storm is created above a specified position with a limited range, targeted similarly to Reaper's Shadow Step. When invoked, it appears above the position as a cloud appearing full of tiny drones, lingering for 8 seconds.

Every 0.25 seconds, a drone appears and immediately attempts to target the nearest enemy. If it successfully finds one, it attempts to lead the target, with a visible laser tracking its aim point - when it thinks it's gotten a lock, it emits a beep and launches itself at the target's anticipated position after a 0.3 second delay.

With careful movement, it is possible to repeatedly dodge the drones and avoid taking damage - think N's Gauss Gun - but the distraction caused by having to do that and attack/heal/etc significantly changes the dynamics of the battlefield.